A process for electroplating chromium to improve the hardness of connector terminals

Abstract

The application relates to the technical field of electroplating, and discloses a chromium electroplating process for improving the hardness of a connector terminal, which comprises the following steps: performing surface pretreatment on the connector terminal, removing surface impurities through ultrasonic cleaning and micro-etching treatment; performing heating treatment on the connector terminal; performing electroplating treatment on the connector terminal by using an electroplating solution comprising trivalent chromium salt, boron nitride nanoparticles, ferroferric oxide nanoparticles, nickel ions, sodium dichromate and chromium alloy additives, so as to form a chromium plating layer; performing passivation treatment on the plating layer; performing low-temperature treatment on the plating layer; and spraying a protective layer on the chromium plating layer. Through the trivalent chromium salt and the sodium dichromate, the trivalent chromium salt is used to reduce hexavalent chromium ions into trivalent chromium, the toxicity of the hexavalent chromium is reduced, the sodium dichromate is used to provide a stable chromium source, the deposition of chromium elements in the electroplating process is ensured, the pollution of hexavalent chromium to the environment and the harm of hexavalent chromium to the health of operators are solved, and the environmental protection and safety of the electroplating process are improved.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, specifically to an electroplating chromium plating process for improving the hardness of connector terminals. Background Technology

[0002] In the electronics industry, connector terminals are a critical component of circuits, and their surface properties are crucial for signal transmission stability and the long-term use of equipment. To improve the wear resistance, corrosion resistance, and electrical contact performance of connector terminals, electroplating technology is widely used in surface treatment. By forming a chromium plating layer on the terminal surface, the hardness of the terminal can be effectively increased, its service life extended, and the stability of signal transmission ensured, meeting the performance requirements of high-end electronic products.

[0003] Currently, trivalent chromium plating is widely used in electroplating processes due to its low cost. However, the hardness of the plating layer formed by this process is limited, failing to meet the stringent standards of electronic products that require high contact stability and durability. Although trivalent chromium plating has economic advantages, its low hardness makes connector terminals prone to wear under frequent use and harsh environmental conditions, thus affecting the stability of signal transmission and the long-term reliability of the equipment.

[0004] To overcome this problem, electroplating solutions using hexavalent chromium instead of trivalent chromium have emerged in the market, aiming to improve the hardness and wear resistance of the plating layer. Hexavalent chromium can form a relatively hard chromium layer during electroplating, significantly improving the hardness and durability of connector terminals. However, the use of hexavalent chromium faces significant environmental issues. Hexavalent chromium is highly toxic and may pose hazards to the environment and the health of operators during use, thus being subject to strict environmental regulations. Furthermore, the cost of hexavalent chromium electroplating is also relatively high, limiting its large-scale promotion and application. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an electroplating chromium plating process for improving the hardness of connector terminals, solving the problems of insufficient hardness in traditional trivalent chromium electroplating and environmental and safety hazards associated with hexavalent chromium electroplating.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an electroplating chromium plating process for improving the hardness of connector terminals, comprising the following steps:

[0007] The connector terminals undergo surface pretreatment, with surface impurities removed through ultrasonic cleaning and micro-etching.

[0008] The connector terminals are heated.

[0009] The connector terminals are electroplated using an electroplating solution containing trivalent chromium salts, boron nitride nanoparticles, iron oxide nanoparticles, nickel ions, and chromium alloy additives to form a chromium plating layer.

[0010] Passivation treatment is applied to the coating;

[0011] The coating is subjected to low-temperature treatment;

[0012] Apply a protective coating to the chrome plating layer.

[0013] Preferably, the concentration of trivalent chromium salt in the electroplating solution is 0.03–0.05 M, the trivalent chromium salt includes one of chromium chloride or chromium sulfate, the concentration of boron nitride nanoparticles is 0.005–0.02 M, the concentration of iron oxide nanoparticles is 0.01–0.05 M, the concentration of nickel ions is 0.005–0.01 M, the concentration of sodium dichromate is 0.1–0.3 M, the concentration of chromium alloy additive is 0.003–0.005 M, and the particle size of the boron nitride nanoparticles is 20–70 nm, the particle size of the iron oxide nanoparticles is 10–50 nm, and the chromium alloy additive includes one of chromium-nickel alloy, chromium-copper alloy, or chromium-molybdenum alloy.

[0014] Trivalent chromium salts: As the primary source of chromium plating, trivalent chromium salts are used to reduce chromium ions to metallic chromium through an electrolytic reduction reaction, which is then deposited onto the surface of the connector terminals to form a chromium plating layer. Compared to hexavalent chromium, trivalent chromium is more environmentally friendly and non-toxic, meeting the requirements of green manufacturing.

[0015] Boron nitride nanoparticles: As a high-hardness material, boron nitride forms a nanocomposite structure in the coating, increasing the coating's hardness and wear resistance. The nanoscale size of boron nitride particles effectively improves the coating's microstructure, enhancing its scratch and wear resistance.

[0016] Ferric oxide nanoparticles: Ferric oxide nanoparticles enhance the hardness and corrosion resistance of the coating. They play a reinforcing role in the coating, reducing its brittleness and improving its overall mechanical properties.

[0017] Nickel ions: The role of nickel ions in electroplating solutions is to stabilize the solution, regulate the crystal structure of the coating, and increase its corrosion resistance and conductivity. The addition of nickel makes the coating denser and improves its wear resistance.

[0018] Sodium dichromate solution: It contains hexavalent chromium ions (Cr). 6+ As the main source of chromium in the electroplating process, it is reduced to metallic chromium (Cr) through an electrolytic reduction reaction. This process can be represented as: Cr 6+ +6e - →Cr 3+Next, metallic chromium (Cr) is deposited onto the metal surface under the influence of an electric current, forming a dense chromium plating layer. This process not only improves the hardness and wear resistance of the connector terminals but also increases the adhesion and corrosion resistance of the plating layer.

[0019] Chromium alloy additives: Chromium alloy additives further enhance the corrosion resistance and hardness of the coating, improve the structure of the coating, and make it more stable in long-term use.

[0020] Preferably, the electroplating solution has a pH value of 4.0-4.5 and a temperature of 35-45℃.

[0021] Preferably, the temperature range of the heat treatment is 70-80°C, and the heating time is 10-15 minutes.

[0022] Heat treatment helps to increase the activity of the metal surface and promotes the uniform deposition of the chromium plating layer. Heating increases surface energy, making the metal surface smoother and more stable, which is beneficial for the adhesion of the plating layer. Heating temperature also helps to reduce stress within the plating layer, improving the overall quality of the plating.

[0023] Preferably, the ultrasonic cleaning uses an ultrasonic cleaning device with an ultrasonic frequency of 40-60 kHz and a cleaning time of 10-15 minutes, and the micro-etching treatment uses a dilute sulfuric acid solution with a micro-etching time of 2-3 minutes and a pH value of 1.5-2.5.

[0024] Ultrasonic cleaning: When using ultrasonic cleaning equipment, the high-frequency vibration of ultrasound can effectively generate cavitation effect, removing impurities such as oil, dirt, and oxide layers adhering to the surface from the terminal surface, improving the surface quality and adhesion of the terminal, and providing good surface conditions for the subsequent electroplating process.

[0025] Micro-etching: When micro-etching is performed using a dilute acid solution, the acid can remove oxides, oxide films, or uneven surface layers on the metal surface, exposing a clean metal substrate. This lays the foundation for good adhesion of the subsequent chromium plating layer and enhances the bonding force between the plating layer and the substrate.

[0026] Preferably, in the electroplating process, a dual-pulse current mode is used, wherein the frequency of the dual-pulse current mode is 50–200 Hz, the duty cycle is 40–60%, and the current density range is 4–6 A / dm³. 2 .

[0027] The dual-pulse current mode, by periodically changing the direction and intensity of the current, helps improve the uniformity and density of the coating, as well as reduce the internal stress of the coating. This mode can promote the uniform distribution of metal deposition on the surface, reduce bubbles or uneven deposition that may occur during electrodeposition, thereby improving the coating quality. The pulsed current can also reduce overpotential, making the coating more uniform and dense, and improving hardness.

[0028] Preferably, the low-temperature treatment temperature is 100-120°C, and the low-temperature treatment time is 30-60 minutes.

[0029] Low-temperature treatment can effectively reduce internal stress in the coating, making its crystal structure more stable. Low-temperature annealing allows metal atoms within the coating to rearrange, improving its microstructure and increasing its hardness, ductility, and durability. Simultaneously, this process can reduce cracks caused by thermal expansion mismatch, thereby enhancing the overall performance of the coating.

[0030] Preferably, the passivation solution includes chromic acid, the passivation time is 10-15 min, and the pH value is 2.5-3.5.

[0031] Passivation treatment forms a thin protective film on the surface of the coating, protecting it from external environmental damage such as oxidation and corrosion. When passivation is performed using chromic acid solution, chromium oxide can form a stable protective layer on the coating surface, preventing the penetration of corrosive media and thus improving the corrosion resistance of the coating.

[0032] Preferably, the concentration of the surfactant in the electroplating solution is 0.01-0.05%, and the surfactant includes one of sodium dodecylbenzenesulfonate, alkylphenol polyoxyethylene ether, or polyvinylpyrrolidone.

[0033] Surfactants help to uniformly disperse particles and optimize coating quality by reducing surface tension in the electroplating solution. During electroplating, surfactants can also improve current density distribution, reduce deposit defects, and make the coating more uniform and smooth. Furthermore, surfactants enhance the wettability of the electroplating solution, further improving the adhesion and stability of the coating.

[0034] Preferably, the protective layer is titanium nitride with a thickness of 0.5 to 1 μm, and is formed by deposition on the surface of the chromium-plated layer using a magnetron sputtering device. The nitrogen flow rate during magnetron sputtering is 10 to 50 sccm, the substrate temperature is 100 to 150°C, and the deposition time is 20 to 40 min.

[0035] The thickness of the titanium nitride protective layer ranges from 0.5 to 1 μm, which ensures the strength and wear resistance of the protective layer without being too thick and causing brittleness of the coating. This ensures the density and uniformity of the sputtered layer, thereby further enhancing the physical properties of the connector terminals, especially their resistance to fatigue, corrosion and wear during long-term use.

[0036] This invention provides an electroplating chromium plating process for improving the hardness of connector terminals. It offers the following advantages:

[0037] 1. This invention utilizes trivalent chromium salts and sodium dichromate to reduce hexavalent chromium ions to trivalent chromium, thereby reducing the toxicity of hexavalent chromium. Furthermore, sodium dichromate provides a stable chromium source, ensuring efficient deposition of chromium during electroplating. This solves the environmental pollution and health hazards of hexavalent chromium to operators, while also improving the environmental friendliness and safety of the electroplating process.

[0038] 2. This invention incorporates boron nitride nanoparticles and iron oxide nanoparticles. During the electroplating process, the boron nitride and iron oxide nanoparticles combine with the coating to form a composite reinforcing phase. The boron nitride particles provide high hardness, while the iron oxide particles enhance the corrosion resistance of the coating. The synergistic effect of the two makes the coating more wear-resistant and scratch-resistant, solving the problem of poor wear resistance of the coating and extending its service life.

[0039] 3. This invention controls the pH value of the electroplating solution to 4.0–4.5. During the electroplating process, H… + Ions can effectively promote the uniform deposition of trivalent chromium ions, thus increasing the uniformity and adhesion of the coating, thereby improving the adhesion strength of the coating and enhancing the stability and corrosion resistance of the coating.

[0040] 4. This invention uses pulses, so the pulsed current can optimize the diffusion rate of metal ions during electroplating, forming a finer grain structure. This increases the density and wear resistance of the coating, thereby improving the fatigue resistance of the coating and achieving high-strength, high-wear-resistant coating deposition.

[0041] 5. This invention sputters titanium nitride onto the surface of a chromium-plated layer. During the sputtering process, nitrogen reacts with titanium metal to form a high-hardness TiN compound layer, which increases the wear resistance and oxidation resistance of the coating, thereby improving the corrosion resistance of the coating and achieving a highly durable and stable surface protection effect. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] To better understand the present invention, the above content will be described in detail below with reference to specific embodiments.

[0045] Please see the appendix Figure 1

[0046] Example 1

[0047] Step 1: Surface Pretreatment

[0048] The connector terminals are first cleaned using an ultrasonic cleaner with an ultrasonic frequency set to 50kHz and a cleaning time of 15 minutes, using a degreasing solution. Afterward, a micro-etching process is performed using a dilute sulfuric acid solution with the pH adjusted to 2.0 for 3 minutes to remove surface impurities and oxides.

[0049] Step 2: Heat treatment

[0050] After cleaning and etching, the terminals are placed in a heating furnace at 75°C for 15 minutes to enhance surface activity and prepare for electroplating.

[0051] Step 3: Electroplating treatment

[0052] The electroplating bath used contained 0.04M trivalent chromium salt, 0.01M boron nitride nanoparticles (50nm particle size), 0.02M iron oxide nanoparticles (30nm particle size), 0.006M nickel ions, 0.2M sodium dichromate, and 0.004M chromium alloy additive. The electroplating bath pH was 4.3, the temperature was maintained at 42℃, a dual-pulse current mode was used with a frequency of 150Hz, a duty cycle of 50%, and a current density of 5A / dm³. 2 The coating thickness is 6μm.

[0053] Step 4: Passivation treatment

[0054] The chromium plating layer was placed in a passivation solution containing chromic acid for 12 minutes, and the pH value was set to 2.8.

[0055] Step 5: Low-temperature treatment

[0056] The terminals are heated to 110°C in a low-temperature furnace for 50 minutes.

[0057] Step Six: Apply a protective layer of titanium nitride.

[0058] Titanium nitride was deposited on the chromium-plated layer using a magnetron sputtering system with a nitrogen flow rate of 30 sccm, a substrate temperature of 120°C, a deposition time of 30 minutes, and a titanium nitride deposition thickness of 0.8 μm.

[0059] Example 2

[0060] Step 1: Surface Cleaning and Micro-etching

[0061] The terminals were ultrasonically cleaned at a frequency of 45 kHz for 12 minutes using a degreasing cleaner. Subsequently, they were micro-etched using a dilute sulfuric acid solution at pH 2.2 for 3 minutes.

[0062] Step 2: Heat treatment

[0063] The terminals are placed in a heating furnace, and the heating temperature is set to 78°C for 15 minutes. Heating increases the surface activity of the metal.

[0064] Step 3: Electroplating treatment

[0065] The electroplating solution used 0.03M trivalent chromium salt, 0.01M boron nitride nanoparticles, 0.01M iron(III) oxide nanoparticles, 0.005M nickel ions, and 0.18M sodium dichromate. The pH of the electroplating solution was 4.2, and the temperature was maintained at 40℃. A dual-pulse current mode was used with a frequency of 100Hz, a duty cycle of 45%, and a current density of 4.5A / dm³. 2 The coating thickness is 7μm.

[0066] Step 4: Passivation treatment

[0067] The passivation solution was chromic acid solution, the passivation time was 10 minutes, and the pH value was 3.2.

[0068] Step 5: Low-temperature treatment

[0069] The low-temperature treatment was carried out at 105°C for 45 minutes.

[0070] Step Six: Applying the Titanium Nitride Protective Layer

[0071] Titanium nitride was applied using magnetron sputtering with a nitrogen flow rate of 25 sccm, a substrate temperature of 115°C, and a deposition time of 35 minutes. The titanium nitride layer thickness was 0.7 μm.

[0072] Example 3

[0073] Step 1: Surface Cleaning and Micro-etching

[0074] The terminals were ultrasonically cleaned at a frequency of 50 kHz for 14 minutes using a degreasing solution. Next, they were micro-etched using a dilute sulfuric acid solution with a pH of 1.9 for 3 minutes.

[0075] Step 2: Heat treatment

[0076] The terminals are placed in the heating furnace, the temperature is set to 80℃, and the heating time is 10 minutes.

[0077] Step 3: Electroplating treatment

[0078] The electroplating solution used contained 0.05M trivalent chromium salt, 0.02M boron nitride nanoparticles (50nm particle size), 0.015M iron(III) oxide nanoparticles (35nm particle size), 0.007M nickel ions, and 0.25M sodium dichromate. The pH of the electroplating solution was adjusted to 4.0, and the temperature was maintained at 44℃. A dual-pulse current mode was used with a frequency of 120Hz, a duty cycle of 55%, and a current density of 6A / dm³. 2 The coating thickness is 6μm.

[0079] Step 4: Passivation treatment

[0080] The passivation treatment used chromic acid solution for 12 minutes at a pH of 3.3.

[0081] Step 5: Low-temperature treatment

[0082] The low-temperature treatment was set to 115℃ for 60 minutes.

[0083] Step Six: Applying the Titanium Nitride Protective Layer

[0084] Titanium nitride was sprayed onto the chromium-plated surface at a nitrogen flow rate of 30 sccm, a substrate temperature of 130°C, and a deposition time of 40 minutes. The titanium nitride deposition thickness was 1 μm.

[0085] Example 4

[0086] Step 1: Surface Cleaning and Micro-etching

[0087] First, the terminals are ultrasonically cleaned at a frequency of 40 kHz for 10 minutes. Then, micro-etching is performed using a dilute sulfuric acid solution with a pH of 2.3 for 3 minutes.

[0088] Step 2: Heat treatment

[0089] After the terminals are cleaned, they are placed in a heating furnace and heated to 70°C for 10 minutes.

[0090] Step 3: Electroplating treatment

[0091] The electroplating solution formulation is as follows: 0.03M trivalent chromium salt, 0.01M boron nitride nanoparticles, 0.01M iron(III) oxide nanoparticles, 0.006M nickel ions, and 0.18M sodium dichromate. The electroplating solution pH is 4.0, the electroplating temperature is 40℃, and a dual-pulse current mode is used with a frequency of 150Hz, a duty cycle of 50%, and a current density of 4.5A / dm³. 2 The coating thickness is 7μm.

[0092] Step 4: Passivation treatment

[0093] The passivation solution was chromic acid solution, the passivation time was 12 minutes, and the pH value was 3.0.

[0094] Step 5: Low-temperature treatment

[0095] The low-temperature treatment was set at 105℃ for 45 minutes.

[0096] Step Six: Apply a protective layer of titanium nitride.

[0097] Titanium nitride was applied using magnetron sputtering at a nitrogen flow rate of 25 sccm, a substrate temperature of 120°C, and a deposition time of 35 minutes. The titanium nitride layer thickness was 0.8 μm.

[0098] Comparative Example 1

[0099] Experimental procedure:

[0100] Surface pretreatment:

[0101] The connector terminals are first ultrasonically cleaned at a frequency of 45kHz for 12 minutes using a degreasing solution.

[0102] The micro-etching process was then performed using a dilute sulfuric acid solution with the pH adjusted to 2.0 for 3 minutes.

[0103] Heat treatment:

[0104] The terminals are placed in the heating furnace, the heating temperature is set to 75℃, and the heating time is 15 minutes.

[0105] Electroplating treatment:

[0106] The electroplating solution used 0.2M sodium dichromate as the chromium source, with a concentration of 0.2M, and no trivalent chromium salts were added.

[0107] Other components include 0.006M nickel ions and 0.004M chromium alloy additives. The electroplating solution was set to pH 4.3, temperature 42℃, and employed a dual-pulse current mode with a frequency of 150Hz, a duty cycle of 50%, and a current density of 5A / dm³. 2 The coating thickness is 6μm.

[0108] Passivation treatment:

[0109] The passivation solution was chromic acid solution, the passivation time was 12 minutes, and the pH value was set to 2.8.

[0110] Low-temperature treatment:

[0111] The low-temperature treatment was carried out at 110°C for 50 minutes.

[0112] Titanium nitride protective coating spraying:

[0113] Titanium nitride was sprayed using a magnetron sputtering system with a nitrogen flow rate of 30 sccm, a substrate temperature of 120°C, a deposition time of 30 minutes, and a titanium nitride layer thickness of 0.8 μm.

[0114] Comparative Example 2

[0115] Experimental procedure:

[0116] Surface pretreatment:

[0117] The terminals are cleaned using ultrasonic cleaning at a frequency of 50kHz for 14 minutes, using a degreasing solution.

[0118] The micro-etching process was then performed using a dilute sulfuric acid solution with the pH adjusted to 2.2 for 3 minutes.

[0119] Heat treatment:

[0120] The terminals are heated to 80°C for 10 minutes.

[0121] Electroplating treatment:

[0122] No boron nitride nanoparticles or iron oxide nanoparticles are added to the electroplating solution; instead, 0.03M trivalent chromium salt, 0.006M nickel ions, and 0.18M sodium dichromate are used.

[0123] The electroplating solution has a pH of 4.3, the electroplating temperature is set at 42℃, a dual-pulse current mode is used with a frequency of 150Hz, a duty cycle of 50%, and a current density of 5A / dm³. 2 The coating thickness is 6μm.

[0124] Passivation treatment:

[0125] The passivation solution was chromic acid solution, the passivation time was 12 minutes, and the pH value was set to 2.8.

[0126] Low-temperature treatment:

[0127] The low-temperature treatment was carried out at 110°C for 50 minutes.

[0128] Titanium nitride protective coating spraying:

[0129] Titanium nitride was sprayed using a magnetron sputtering system with a nitrogen flow rate of 30 sccm, a substrate temperature of 120°C, a deposition time of 30 minutes, and a titanium nitride layer thickness of 0.8 μm.

[0130] Comparative Example 3

[0131] Experimental procedure:

[0132] Surface pretreatment:

[0133] The terminals were cleaned using an ultrasonic cleaning device at a frequency of 40kHz for 10 minutes.

[0134] Subsequently, micro-etching was performed using a dilute sulfuric acid solution with a pH value set to 2.3 and a processing time of 3 minutes.

[0135] Heat treatment:

[0136] The terminals are heated to 80°C for 15 minutes.

[0137] Electroplating treatment:

[0138] The electroplating solution uses 0.05M trivalent chromium salt, 0.02M boron nitride nanoparticles, 0.015M iron oxide nanoparticles, 0.007M nickel ions, and 0.25M sodium dichromate. The pH of the electroplating solution is 4.0, and the electroplating temperature is maintained at 44℃.

[0139] This experiment does not use pulsed current mode, but rather continuous current mode, with a current density set to 6 A / dm². 2 The coating thickness is 6μm.

[0140] Passivation treatment:

[0141] The passivation solution was chromic acid solution, the passivation time was 12 minutes, and the pH value was set to 3.3.

[0142] Low-temperature treatment:

[0143] The low-temperature treatment was carried out at 115°C for 60 minutes.

[0144] Titanium nitride protective coating spraying:

[0145] Titanium nitride was sprayed using a magnetron sputtering system with a nitrogen flow rate of 30 sccm, a substrate temperature of 130°C, a deposition time of 40 minutes, and a titanium nitride layer thickness of 1 μm.

[0146] Comparative Example 4

[0147] Experimental procedure:

[0148] Surface pretreatment:

[0149] The terminals are cleaned using an ultrasonic cleaning device at a frequency of 40kHz for 10 minutes.

[0150] Subsequently, a dilute sulfuric acid solution was used for micro-etching, with the pH value adjusted to 2.3 and the etching time being 3 minutes.

[0151] Heat treatment:

[0152] The terminals are heated to 78°C for 15 minutes.

[0153] Electroplating treatment:

[0154] The electroplating solution used 0.03M trivalent chromium salt, 0.01M boron nitride nanoparticles, 0.01M iron oxide nanoparticles, 0.005M nickel ions, and 0.18M sodium dichromate. The pH of the electroplating solution was 4.3, the electroplating temperature was maintained at 42℃, and a dual-pulse current mode was used with a frequency of 150Hz, a duty cycle of 50%, and a current density of 5A / dm³. 2 The coating thickness is 6μm.

[0155] Passivation treatment:

[0156] The passivation solution was chromic acid solution, the passivation time was 12 minutes, and the pH value was set to 3.0.

[0157] Low-temperature treatment:

[0158] In this comparative example, the low-temperature treatment step is omitted, and passivation treatment is performed directly.

[0159] Titanium nitride protective coating spraying:

[0160] Titanium nitride was sprayed using a magnetron sputtering system with a nitrogen flow rate of 25 sccm, a substrate temperature of 120°C, a deposition time of 35 minutes, and a titanium nitride layer thickness of 0.8 μm.

[0161] Experiment 1: Comparison of Hardness and Wear Resistance of Electroplated Layers

[0162] Experimental steps:

[0163] Sample preparation:

[0164] Samples were prepared according to Example 1 and Comparative Example 1. Example 1 used an electroplating solution containing 0.04 M trivalent chromium salt and 0.2 M sodium dichromate, and the coating thickness after electroplating was 6 μm; Comparative Example 1 used an electroplating solution containing 0.2 M sodium dichromate, without using trivalent chromium salt, and the coating thickness was also 6 μm.

[0165] Hardness test:

[0166] Each sample was tested using a Vickers hardness tester. A standard load (100g) was applied, and the surface hardness of the sample was tested at three different locations, with the average value taken.

[0167] Abrasion resistance test:

[0168] The sample surface was abraded using a Taber abrasion tester with a pressure of 500g and a rotation speed of 1000 rpm. The mass loss of the sample after abrasion was recorded. Different abrasion wheels (#1000, #4000) were used for testing to ensure the accuracy of the comparative data.

[0169] Data Records:

[0170] Experimental data table

[0171] Table 1: Comparison of Hardness and Abrasion Resistance of Electroplated Coatings

[0172]

[0173] Experiment Summary:

[0174] The experimental data show that Example 1 and Comparative Example 1 have significant differences in hardness and wear resistance, further verifying the advantages of the present invention in improving coating quality.

[0175] First, in the hardness test, the hardness values ​​of Example 1 were generally higher than those of Comparative Example 1. The hardness of Example 1 was 750 HV, 780 HV, and 765 HV in three tests, while the hardness of Comparative Example 1 ranged from 640 HV to 655 HV. The average hardness value of Example 1 was significantly higher than that of Comparative Example 1, indicating that the coating hardness was significantly improved after using the formulation of trivalent chromium salt and sodium dichromate. The reason for the increased hardness may be related to the stable chromium source provided by the trivalent chromium salt and its reduction reaction, which makes the crystal structure of the coating more compact, thereby enhancing the compressive strength and hardness of the coating.

[0176] In the wear resistance test, the wear amount of Example 1 was generally lower than that of Comparative Example 1. In the test using a #1000 wear wheel, Example 1 showed wear amounts of 0.12 mg, 0.10 mg, and 0.07 mg, respectively, while Comparative Example 1, under the same test conditions, showed wear amounts of 0.18 mg, 0.20 mg, and 0.22 mg, indicating a significantly higher wear amount. Especially when using a #4000 wear wheel, Example 1 showed even lower wear amounts, demonstrating the superior performance of the coating under fine-grained wear conditions. The lower wear amount of Example 1 is directly related to its higher hardness value, proving that the use of trivalent chromium salts improves the wear resistance and scratch resistance of the coating.

[0177] The data also show that, under the same electroplating process conditions (e.g., pH of the plating solution is 4.3, plating temperature is 42℃, and dual-pulse current mode), Example 1 not only exhibits excellent hardness and wear resistance but also demonstrates significant advantages in stability. The electroplating solution in Comparative Example 1, which did not use trivalent chromium salts, showed inferior hardness and wear resistance compared to Example 1, further validating the crucial role of trivalent chromium salts in improving coating quality.

[0178] In summary, by comparing the experimental data, Example 1 demonstrates a significant advantage over Comparative Example 1 in improving the hardness, wear resistance, and uniformity of the coating using a trivalent chromium salt and sodium dichromate formulation. These data indicate that the present invention, by optimizing the selection of the chromium source, can effectively improve coating performance while reducing the toxicity of hexavalent chromium, ensuring the environmental friendliness and safety of the electroplating process.

[0179] Experiment 2: Comparison of coating adhesion and uniformity

[0180] Experimental steps:

[0181] Sample preparation:

[0182] Example 2: The electroplating solution contained 0.03M trivalent chromium salt, 0.01M boron nitride nanoparticles, 0.01M iron oxide nanoparticles and 0.18M sodium dichromate, and the coating thickness was 7μm.

[0183] Comparative Example 2: The electroplating solution did not contain boron nitride nanoparticles or iron oxide nanoparticles. 0.03M trivalent chromium salt and 0.18M sodium dichromate were used, and the coating thickness was also 7μm.

[0184] Adhesion test:

[0185] The adhesion of the sample is measured using a pull-off test. The pull-off device is attached to the coating surface, and then pulled out by the device; the maximum peel force is recorded.

[0186] Each sample underwent at least three pull-out tests, and the average value was used for analysis.

[0187] Uniformity test:

[0188] The sample surface was observed using a scanning electron microscope (SEM). The uniformity of the coating, surface finish, and changes in coating thickness were observed.

[0189] By comparing the surface structures of Example 2 and Comparative Example 2, the uniformity and microstructure of the coating were evaluated.

[0190] Data Records:

[0191] Adhesion and uniformity test results were recorded. Pull-out force values ​​were analyzed with microscopic images to evaluate the impact of the two electroplating solution formulations on coating quality.

[0192] Experimental data table

[0193] Table 2: Comparison of Coating Adhesion and Uniformity Data

[0194]

[0195] Experiment Summary:

[0196] The experimental data clearly show that the coating adhesion and uniformity of Example 2 are superior to those of Comparative Example 2. In the adhesion test, the average adhesion value of Example 2 was 46.3 MPa, while the average adhesion value of Comparative Example 2 was only 37.0 MPa. This difference indicates that the addition of boron nitride nanoparticles and iron oxide nanoparticles to the electroplating solution can significantly enhance the adhesion of the coating, suggesting that the combination of these two nanoparticles with the coating forms a composite reinforcing phase, improving the overall stability and peel resistance of the coating.

[0197] The uniformity test results also showed a similar trend. Example 2 showed a higher coating uniformity score (4.5), while Comparative Example 2 showed a lower uniformity score (3.7). SEM images revealed that the coating surface of Example 2 was smoother and had a more uniform thickness distribution, indicating that the addition of nanoparticles improved both the hardness and structural uniformity of the coating. In contrast, the coating of Comparative Example 2 exhibited an uneven surface and localized thickness variations, which may be related to the lack of reinforcing effects from boron nitride and iron oxide nanoparticles.

[0198] Therefore, the addition of nanoparticles not only enhances the mechanical properties of the coating but also improves its quality, resulting in stronger adhesion and uniformity. This improvement is particularly significant in applications requiring high hardness and adhesion. In contrast, Comparative Example 2, without added nanoparticles, shows significantly inferior coating performance and stability, failing to deliver the same superior results as Example 2.

[0199] Experiment 3: Comparison of Coating Corrosion Resistance

[0200] Experimental steps:

[0201] Sample preparation:

[0202] Example 3: The electroplating solution contains 0.05M trivalent chromium salt, 0.02M boron nitride nanoparticles, 0.015M iron oxide nanoparticles and 0.25M sodium dichromate, and the coating thickness is 6μm.

[0203] Comparative Example 3: The electroplating solution used 0.05M trivalent chromium salt, 0.02M boron nitride nanoparticles, 0.015M iron oxide nanoparticles and 0.25M sodium dichromate, and the coating thickness was 6μm, but no low temperature treatment was performed.

[0204] Corrosion resistance test:

[0205] A salt spray test was conducted by placing the sample in a salt spray chamber under the conditions of 5% NaCl solution and a temperature of 35°C for 48 hours.

[0206] Observe the corrosion of the coating, record the peeling, rust, and surface damage of the sample, and quantify the corrosion area.

[0207] Antioxidant test:

[0208] An oxidation test was performed by exposing the coating sample to a high-temperature air environment at 100°C for 72 hours.

[0209] Record whether there are signs of oxidation on the sample surface, changes in coating color, and surface damage.

[0210] Data Records:

[0211] Experimental data table

[0212] Table 3: Comparison of Corrosion Resistance and Oxidation Resistance of Coatings

[0213]

[0214]

[0215] Experiment Summary:

[0216] By comparing the salt spray and oxidation test results of Example 3 and Comparative Example 3, it is clear that low-temperature treatment significantly improves the corrosion resistance and oxidation resistance of the coating. The average corrosion area in the salt spray test for Example 3 was 9%, while that for Comparative Example 3 was 20%. This difference indicates that low-temperature treatment helps reduce the internal stress of the coating, making it more stable and less prone to cracking or peeling, thus improving its corrosion resistance.

[0217] The results of oxidation tests also confirmed this. The average color change (ΔE) value of Example 3 was 3.3, while the ΔE value of Comparative Example 3 was 5.6, indicating a significantly higher degree of oxidation in the latter. Low-temperature treatment, by optimizing the microstructure of the coating, reduced lattice defects and enhanced the coating's oxidation resistance, thereby reducing the degree of oxidation and discoloration.

[0218] Therefore, cryogenic treatment plays a crucial role. By treating the coating at low temperatures, the metal atoms within the coating rearrange, reducing internal stress and improving its stability and corrosion resistance. Simultaneously, this process helps prevent oxide formation and reduces coating aging. Thus, cryogenic treatment significantly improves the overall durability of the coating, especially demonstrating a stronger advantage when facing high-temperature and corrosive environments.

[0219] Experiment 4: Comparison of Environmental Protection and Safety in Electroplating Processes

[0220] Experimental steps:

[0221] Sample preparation:

[0222] Example 4: The electroplating solution contained 0.03M trivalent chromium salt, 0.01M boron nitride nanoparticles, 0.01M iron oxide nanoparticles and 0.18M sodium dichromate, and the coating thickness was 6μm.

[0223] Comparative Example 4: 0.2M sodium dichromate was used in the electroplating solution, without the addition of trivalent chromium salts, and the coating thickness was 6μm.

[0224] Hexavalent chromium content test:

[0225] During the electroplating process, the concentration of hexavalent chromium in the electroplating waste liquid was periodically sampled and analyzed using a UV-Vis spectrophotometer. The test wavelength was 373 nm, and the concentration of hexavalent chromium in the waste liquid was calculated.

[0226] Each group of experiments was tested 3 times, and the concentration of hexavalent chromium was recorded.

[0227] Wastewater treatment efficiency test:

[0228] Hexavalent chromium was reduced to trivalent chromium using a chemical reduction method, with sodium sulfite (Na₂SO₃) added as the reducing agent. The removal rate was calculated by monitoring changes in the concentration of hexavalent chromium in the wastewater.

[0229] The concentration of heavy metal ions in the wastewater was detected using an ion chromatograph (IC), and the changes in the concentration of hexavalent chromium before and after removal were recorded.

[0230] Data Records:

[0231] Record the concentration of hexavalent chromium and the removal rate of hexavalent chromium in wastewater in each group of experiments, and compare them.

[0232] Experimental data table

[0233] Table 4: Comparison of Hexavalent Chromium Concentration and Wastewater Treatment Removal Rate

[0234]

[0235] Experiment Summary:

[0236] By comparing the experimental data on hexavalent chromium concentration and wastewater treatment efficiency of Example 4 and Comparative Example 4, the results show that using trivalent chromium salts instead of hexavalent chromium salts can significantly improve the environmental friendliness of the electroplating process. In Example 4, the concentration of hexavalent chromium in the electroplating wastewater remained at a low level, and the removal rate after wastewater treatment reached over 95%. In contrast, the concentration of hexavalent chromium in Comparative Example 4 was higher, and the removal rate after wastewater treatment was only about 70%. Obviously, the use of trivalent chromium salts reduced the release of hexavalent chromium and had a smaller impact on the environment.

[0237] This difference can be explained by mechanism. Trivalent chromium salts have lower toxicity and higher stability, and do not easily decompose into hexavalent chromium during electroplating, thus effectively controlling the concentration of hexavalent chromium in the electroplating solution. Simultaneously, the introduction of trivalent chromium salts significantly reduces the concentration of hexavalent chromium in the electroplating wastewater, providing greater convenience for subsequent wastewater treatment. In contrast, the use of hexavalent chromium salts leads to a high concentration of hexavalent chromium during electroplating, increasing the difficulty of removing hexavalent chromium from wastewater.

[0238] From the perspective of wastewater treatment effectiveness, the use of trivalent chromium salts further improved the efficiency of wastewater treatment. In the experiments, the removal rate of hexavalent chromium in Example 4 exceeded 90%, while the removal rate in Comparative Example 4 was generally below 70%. This indicates that the use of trivalent chromium salts not only reduced the concentration of hexavalent chromium in the wastewater but also improved the efficiency of wastewater treatment, significantly reducing the environmental pollution caused by hexavalent chromium.

[0239] In summary, this invention, by using trivalent chromium salts instead of hexavalent chromium salts, not only improves the environmental friendliness and safety of the electroplating process but also enhances wastewater treatment efficiency, contributing to a greener and more environmentally friendly electroplating process. This innovation significantly improves the overall performance of the electroplating process while reducing environmental pollution and increasing the stability of the electroplating solution.

[0240] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A chromium plating process for improving the hardness of connector terminals, characterized in that, Includes the following steps: The connector terminals undergo surface pretreatment, with surface impurities removed through ultrasonic cleaning and micro-etching. The connector terminals are heated. The connector terminals are electroplated using an electroplating solution containing trivalent chromium salts, boron nitride nanoparticles, iron oxide nanoparticles, nickel ions, sodium dichromate, and chromium alloy additives to form a chromium plating layer. Passivation treatment is applied to the coating; The coating is subjected to low-temperature treatment; Apply a protective coating to the chrome plating layer; The electroplating solution contains a trivalent chromium salt concentration of 0.03–0.05 M, which includes either chromium chloride or chromium sulfate. The concentration of boron nitride nanoparticles is 0.005–0.02 M, the concentration of iron oxide nanoparticles is 0.01–0.05 M, the concentration of nickel ions is 0.005–0.01 M, the concentration of sodium dichromate is 0.1–0.3 M, and the concentration of chromium alloy additives is 0.003–0.005 M. The boron nitride nanoparticles have a particle size of 20–70 nm, the iron oxide nanoparticles have a particle size of 10–50 nm, and the chromium alloy additives include either a chromium-nickel alloy, a chromium-copper alloy, or a chromium-molybdenum alloy. The ultrasonic cleaning uses an ultrasonic cleaning device with an ultrasonic frequency of 40-60 kHz and a cleaning time of 10-15 minutes. The micro-etching treatment uses a dilute sulfuric acid solution with a micro-etching time of 2-3 minutes and a pH value of 1.5-2.

5. In the electroplating process, a dual-pulse current mode is used, wherein the frequency of the dual-pulse current mode is 50-200Hz, the duty cycle is 40-60%, and the current density range is 4-6A / dm². The low-temperature treatment is performed at a temperature of 100–120°C for a duration of 30–60 minutes.

2. The electroplating chromium plating process for improving the hardness of connector terminals according to claim 1, characterized in that, The electroplating solution has a pH value of 4.0-4.5 and a temperature of 35-45℃.

3. The electroplating chromium plating process for improving the hardness of connector terminals according to claim 1, characterized in that, The temperature range of the heat treatment is 70-80℃, and the heating time is 10-15 minutes.

4. The electroplating chromium plating process for improving the hardness of connector terminals according to claim 1, characterized in that, The passivation solution includes chromic acid, the passivation time is 10-15 min, and the pH value is 2.5-3.

5.

5. The electroplating chromium plating process for improving the hardness of connector terminals according to claim 1, characterized in that, The concentration of the surfactant in the electroplating solution is 0.01-0.05%, and the surfactant includes one of sodium dodecylbenzenesulfonate, alkylphenol polyoxyethylene ether, or polyvinylpyrrolidone.

6. The electroplating chromium plating process for improving the hardness of connector terminals according to claim 1, characterized in that, The protective layer is titanium nitride with a thickness of 0.5 to 1 μm, and is formed by deposition on the surface of the chromium-plated layer using a magnetron sputtering device. The nitrogen flow rate during magnetron sputtering is 10 to 50 sccm, the substrate temperature is 100 to 150°C, and the deposition time is 20 to 40 min.

Images